To trust no man but one, and trust him too much — this captures Tiberius’s behavior in a nutshell. Clearly he overextended Sejanus’s loyalty. Given that the question of the succession remained open, Sejanus seems to have found the temptation too great to resist: Not content with being the emperor’s virtual equal, he strove to become emperor himself. The report of the conspiracy is said to have been delivered to Tiberius by a trusted slave of Antonia Minor, who as his sister-in-law had privileged access to the emperor. The old man rallied to bring off one bravura performance. He secretly appointed a new Praetorian prefect, Quintus Naevius Macro, simultaneously ordering that ships be made ready to carry him away to safety in case of emergency, to a garrison of loyal troops. Then in a dramatic denouement in the Senate, a letter was read aloud in Sejanus’s presence; it began with noncommittal phrases, but finally accused him directly of plotting against the emperor. The once all-powerful favorite was executed the same day, along with his children. Their bodies were dragged through Rome for several days after that.
A new spate of trials for treason ensued, as people settled old scores and used new openings to try to make a name for themselves. In the year 33 Tiberius gave orders that everyone in prison for participating in the conspiracy was to be killed. “On the ground lay the huge hecatomb of victims: either sex, every age; the famous, the obscure,” writes Tacitus, “scattered or piled in mounds. Nor was it permitted to relatives or friends to stand near, to weep over them, or even to view them too long; but a cordon of sentries, with eyes for each beholder’s sorrow, escorted the rotting carcasses as they were dragged to the Tiber, there to float with the current or drift to the bank, with none to commit them to the flames or touch them. The ties of our common humanity had been dissolved by the force of terror; and before each advance of cruelty compassion receded” (Tac. Ann. 6.19.2–3).
At this point the relationship between the emperor and the aristocracy had reached a nadir. Both sides were extremely fearful after the events surrounding the fall of Sejanus. Those who had nothing left to lose circulated denunciations and scurrilous attacks. The emperor furnished publicity to the universal hatred that befell him, by having such tracts read aloud at their authors’ indictment before the Senate. A letter Tiberius sent to the Senate, whose opening passage is cited by both Tacitus and Suetonius, vividly captures the situation near the end of his reign. It also displays the harrowing and helpless frankness so characteristic of him: “If I know what to write to you, Senators, or how to write it, or what to leave unwritten at present, may all gods and goddesses visit me with more destruction than I feel that I am daily suffering” (Tac. Ann. 6.6.1; Suet. Tib. 67.1). All communication between the emperor and the aristocracy had broken down. When the seventy-eight-year-old man, who no longer dared set foot in his home city, finally died, the Romans shouted, “Tiberius into the Tiber!” (“Tiberium in Tiberim!” Suet. Tib. 75.1).
The social conditions encountered by a young man growing up in aristocratic circles in Rome during the rule of Tiberius could not have been less suited to fostering humanity. The emperor had unlimited powers and his orders had to be carried out without hesitation; at the same time he was hated and lived in constant fear of conspiracies. Many aristocrats were utterly without scruples; they would denounce each other but bow and scrape to the emperor, all the while waiting for the next opportunity to conspire against him. Murders and executions were everyday occurrences, and ultimately an ambiguity in communication with which the actual circumstances were covered over, lacking all candor and honesty, and thus further intensifying the general anxiety and uncertainty. How did Caligula fare as an adolescent in such a society?
The death of Germanicus in the year 19 rid Tiberius of a potential problem in the succession. His biological son Drusus (II) was by virtue of his age the only eligible aspirant for the throne at the time. The following years would reveal, however, that the acquisition of dynastic prestige by one branch or the other of the imperial family could always become a political problem, either because it aroused the ambitions of other family members or because third parties were able to exploit latent rivalries.
Sejanus’s position as the emperor’s trusted confidant made him a rival of Drusus early on. The sources report that in the year 23 he began an affair with Drusus’s wife, Livilla, who was a sister of Germanicus, and persuaded her to poison her husband. Evidently the charge was clearly proved in a trial eight years later, after the Praetorian prefect’s fall from favor. It is highly improbable that Sejanus had ambitions of seizing the throne himself at that time; more likely he was concerned about securing his own future if Tiberius should die. The emperor was then already over sixty, and his death would have put Sejanus in a most precarious position in the event of Drusus’s succession.
After Drusus II died, the popular family of Germanicus — his widow, Agrippina, and her sons — immediately regained their central place in speculation about the succession. In a session of the Senate Tiberius particularly recommended Nero and Drusus (III), by then seventeen and sixteen years of age, to the senators, and in so doing offered official confirmation of their importance. Ten-year-old Caligula, by contrast, seemed of less interest because of both his age and his two older brothers. For a time this situation would prove a great advantage. The very next year it emerged that the senators had taken Tiberius’s recommendation too literally; they heaped so many honors on Nero and Drusus that the emperor complained, perhaps because he felt a bit neglected himself. Furthermore his relationship with Agrippina was deteriorating, a development that the sources attribute mainly to intrigues set in motion by Sejanus. After the death of Drusus (II), Tiberius is said to have thought about eliminating Agrippina and her sons as well. According to Tacitus this plan failed for two reasons: The guards in the house of Germanicus’s family were alert and Agrippina was too chaste for Sejanus to use his apparent charms on her. Thereupon he prevailed upon Livia and Livilla to inform Tiberius that the mother of the two possible successors was ambitious for power. Moreover Sejanus denounced her to the emperor himself, saying that Agrippina was gathering a political faction around her that threatened to divide the citizenry.
The next step — denouncing those who still dared to frequent the family’s house — drew on the assistance of compliant senators. The charge was crimes against the lex maiestatis, as in the particularly nasty case of Titius Sabinus described above. When things went so far that even one of Agrippina’s cousins was accused, Agrippina went to Tiberius to demand an explanation, and he accused her openly of a lust for power. Sejanus then made use of the atmosphere prevailing at the time, in the truest sense utterly poisoned, to mount a classic intrigue. Through intermediaries he convinced Agrippina that Tiberius was planning to poison her, and that she should avoid having anything to eat at the house of her adoptive father-in-law. When she was invited soon thereafter to a banquet at which Livia was also present, the emperor noticed that she ate nothing. (He may possibly have been informed of Agrippina’s suspicions.) He praised the fruit that was just then being served, selected a piece, and handed it to her himself. This gesture only heightened her fears, so she passed the fruit to a slave in her retinue without tasting it. Tiberius is said to have turned to Livia and remarked that it would be no wonder if he were to adopt even harsher measures against Agrippina, since she thought he was trying to poison her.